Multiplexing involves the coding and subsequent decoding of several channels of information for transmission over a single line or communication link. For critical applications, the standard single line data bus commonly used in multiplexing systems is not suitable. When all systems and circuits are put on one line, the integrity of these systems is comprised by damage to this one line or bus. Therefore, multiple sets of data lines in physically separated locations carrying the same data are used. The redundancy of data lines is appealing in automotive electrical systems because of damage susceptibility and attendant safety implications. Virtually all multiplex systems which have been applied to automotive systems consume significant quiescent current, thereby causing undesirable battery drain.
One such redundant multiplexing system uses multiple input lines which are split and sensed by a pair of independent multiplexers. Each multiplexer sends its output to a separate demultiplexer, and the multiple outputs from the pair of demultiplexers are then combined. The U.S. Pat. No. 3,940,566 issued Feb. 24, 1976 in the name of Jeppsson et al discloses such a system where separate multiplexers and demultiplexers are used for redundancy purposes. A problem with such an assembly is the expense involved with each additional multiplexer and demultiplexer. Also, data transmission problems arise if faults occur to the communication line.